1. Field of the Invention
The invention relates to a process for the preparation of an alkyl 2-(2,2-dihalovinyl)-3,3-dimethylcyclopropylacetate.
2. Description of the Prior Art
These compounds are useful as intermediate in the preparation of insecticidally active compounds starting from (+) 3-carene. These insecticidally active compounds are of the pyrethrin type and may, therefore, be called "pyrethroids". As these pyrethroids combine exceptionally good insecticidal properties with a very low mammalian toxicity, they are of great interest to the agrochemical industry and considerable effort has been directed at finding economic routes for their production. The esters of the 2-(2,2-dihalovinyl)-3,3-dimethylcyclopropanecarboxylic acids (hereinafter 2-(2,2-dichlorovinyl)-3,3-dimethylcyclopropanecarboxylic acid will also be referred to as "compound H") described in U.S. Pat. No. 4,024,163 are examples of pyrethroids. Compound H has the following structural formula: ##STR1## 3-Carene can, owing to the asymmetrical configurations at the 1- and 6-positions of the molecule, exist in the form of two optically active isomers, the (+) and the (-) configuration. The (+) configuration is an inexpensive, readily available, naturally occurring terpene found in numerous varieties of pine trees; it can be easily purified by fractional distillation.
The Applicants have found a simple process to prepare the above-mentioned intermediates in high yield.